Soil Microbial Ecology - Soil Molecular Ecology Laboratory

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E X E R C I S E
7
SOIL ALGAE ENUMERATION
OBJECTIVE:
Quantify algal populations using the most probable number technique and enzymatically
quantify soil metabolic activity by using phosphatase assay.
ALGAE TEST
Since algae are photoautotrophs, they can be grown on selective culture media devoid of
organic carbon. This eliminates competing microbes, which would outgrow the algae
and possibly inhibit their development. One can make these media further selective for
cyanobacteria (blue-green algae) by eliminating all sources of fixed nitrogen (ammonium
or nitrate etc.). Enumeration of soil algae is most frequently accomplished by a dilution
technique involving inoculation of replicate tubes of an appropriate liquid medium with
subsamples from the dilution tubes. This technique is known as the most probable
number technique and represents a statistical probability approach to counting
microorganisms. It is employed when the group of organisms being investigated is not
readily cultured on solid media.
MATERIALS:
Soil samples - forest and agriculture
Modified Bristol’s solution (9 ml per test tube) - (NaNO 3 , 0.25 g; CaCl 2 , 0.025 g;
MgS0 4 .7H 2 O , 0.075 g; K 2 HPO 4 , 0.075 g; KH 2 PO 4 , 0.018 g; NaCl , 0.025 g; FeCl 3 ,
0.01 g; NaMoO 4 .2H 2 O , 0.002 g; and trace minerals* , 1ml combined and bring the
volume with distilled water to 1 L. *Trace element stock solution: MnSO 4 , 2.1 g;
H 3 BO 3 , 2.8 g; Cu (NO 3 ) 2 .3H 2 O , 0.4 g; ZnSO 4 . 7H 2 O , 0.24 g combined and bring
the volume with distilled water to 1 L. Use 1 ml stock solution per liter of medium
Sterile water blanks, 90 and 9 ml
Sterile pipettes, 1 ml
Test tube racks